Reference is made to FIG. 1 which illustrates a conventional current reference generator circuit 10. The circuit 10 includes an operational amplifier 12 having a non-inverting (positive) input 14 and an inverting (negative) input 16. The non-inverting input 14 is configured to receive a reference voltage. In an exemplary implementation, the reference voltage is a bandgap reference voltage (VBG) generated by a bandgap voltage generator circuit (known to those skilled in the art). The amplifier 12 is powered from the positive and negative voltage supply nodes, in this case indicated as the voltage Vana3V3 (an analog circuit supply voltage for example of 3V) and ground. The amplifier includes an output node 18 coupled to the gate of a transistor 20. The transistor 20 is an n-channel MOSFET device. The source-drain path of the transistor 20 is coupled between the positive and negative voltage supply nodes. A transistor 22 has a source-drain path coupled in series with the transistor 20. The transistor 22 is a p-channel MOSFET device configured as a diode-connected device with its gate terminal connected to its drain terminal (this device supporting current replication and scaling through mirroring circuits as known in the art). The source terminal of transistor 22 is coupled to the positive voltage supply node. The source terminal of transistor 20 is coupled through a feedback path 24 to the inverting input 16 of the amplifier 12. A resistor 26 is coupled between the source terminal of transistor 20 (the inverting input 16 of amplifier 12) and the negative voltage supply node. The operational amplifier 12, through the negative feedback path 24, functions to drive the operation of the transistor 20 such that the voltage at the source terminal of transistor 20 equals the bandgap reference voltage (VBG). A reference current Iref (=VBG/R1) is accordingly generated in the source-drain path of transistor 20 through the resistor 26.
The spread of the bandgap reference voltage (VBG) is typically very small. However, the resistance of resistor R1 is dependent on process corner, and the spread of the resistance value with process variation may be higher than ±30%. This can lead to significant errors in the reference current generation. An improved current reference circuit that is better temperature and process compensated is needed.